16 active low buttons and 2 Analog joysticks
Supports NXT-G, RobotC and NXC/NBC.
Send joystick commands & button presses to NXT
Maximum power consumption: 15mA at 4.7V (while communicating with PS2 controller)
The joystick utilized one of the sensor ports on the NXT brick, and plugged directly into port 2. It required connection buttons to be selected on the sensor port section and on the controller itself (middle most button on controller and the white button on bottom right item in picture below.) The analog button was also required to be activated so the control stick potentiometers could be utilized. See picture below for reference to items.
Fig. 2-14 Wireless Controller, Receiver, and NXT Adapter
2.2.5 Technical Trouble/Troubleshooting
Most technical trouble will be encountered in the software section for the base group. The mechanical and structural part is pretty straight forward.
For the most part, you will want to meet on a regular basis with both the head and the arm groups. The base will be needing information from both of them, and if they make any dimensional changes, it will impact what you need to design in order to accommodate. We met monthly with the other teams just to make sure our designs and their designs were compatible.
2.3.1 Hardware introduction
The arm portion of the project involves using an existing head and neck and modifying an existing mobile base. The arm, however, is designed and built from scratch. For this reason, the majority of work on the arm in the first phase revolves around its mechanical design and construction.
The first step in the mechanical design of the arm is to define its degrees of freedom. A degree of freedom, or DOF, is an independent displacement associated with a particular joint. Joints can be ether prismatic or revolute, or both. Prismatic joints are capable of linear motions while revolute joints are capable of rotating. In this case each of the arm’s joints is revolute, and thus, each degree of freedom is a rotation. Each of these DOFs is controlled by an actuator.
2.3.2 Mechanical Design and Components
The human arm is considered to have seven degrees of freedom. These consist of three rotations at the shoulder, one at the elbow, and three rotations at the wrist. The actuators that control the shoulder and, to a lesser degree, the elbow have to carry the load of the entire arm, hand, and payload. These actuators must be capable of producing substantially greater torque than actuators at other joints. To reduce the number of high-torque actuators required, the shoulder is designed with only two DOFs. Although the wrist does not have to carry a high load like the shoulder, space at this point on the arm is limited. For this reason, the wrist is given only two DOFs. This leaves a total of five degrees of freedom for the arm instead of seven. The human hand has twenty seven degrees of freedom, most of which are associated with the fingers. To grasp a simple object, the motions of the fingers are not needed. This assumption allows the hand to be designed with one degree of freedom, thus greatly simplifying the design. A simple representation of the arm is shown in the Figure 2-15 below. The red arrows represent the axis that each DOF can rotate about. Although the hand is shown, its DOF is not labeled.
Fig. 2-15: Robot arm’s degrees of freedom.
As mentioned above, it is important that the final robot design be easy to reproduce and mirror. This is facilitated by using TETRIX components whenever possible. TETRIX is a component system originally designed for use in high school robotics competitions. The system consists of a variety of prefabricated aluminum components that are designed to be easily modified and connected to one another. Also included are high torque DC gear motors, servos, and motor drivers. These components are compatible with the LEGO Mindstorms system. The LEGO system not only includes components for building robots, but includes a series of Plug ‘N Play sensors and peripherals in addition to a controller and programming environment. Together these systems allow a designer to quickly build robot prototypes with little or no fabrication. The details of the LEGO controller, programming environment, and electronic components are described in later sections. Figure 2-16 shows the basic TETRIX robotics kit.